Date: Sep 2008
NV Version: all
OS Version: Unix/ LINUX
Symptoms:
Negative compression has been seen when backing up data after changing block size. In attempt to clarify this we ran some tests and below are the results.
Conclusion of tests:
Ran tests to check if having a 256KB block size changed the compression ratio. On a 617GB backup of flat files to LT03 tape the findings were:
256KB block size, Data backed up 617GB, compression ratio 3.636:1, time taken 2h 32 mins, trans_rate 69.36Ms
32KB block size, Data backed up 617GB, compression ratio 3.629:1, time taken 3h 10 mins, trans_rate 55.61Ms
This tells us that increasing the block size should not have an adverse effect on compression and should increase the speed of the backup. So we can conclude that if there is an adverse effect by changing the block size this will be down to a combination of type of file + block size or there is a problem with the tape drive.
Certain files do not compress well and if comp
Please refer to the text above
